Sealing rings of this type are typically seated in an annular recess of the bore wall, sealing with a radially-inwardly directed sealing lip against an axially-smooth surface of a rod. This is called a "rod seal". However, the invention is also relevant to "piston seals", i.e. a situation in which the sealing ring is seated in an annular recess of the rod, sealing with a radially-outwardly directed sealing lip against an axially-smooth surface of the bore.
The present concept is particularly concerned with single-acting sealing rings, i.e. for handling high pressure from one axial direction only and therefore having in effect a high-pressure side and a low-pressure side. However the invention may have some application with sealing rings in other contexts.
A conventional single-acting sealing ring is a one-piece elastomeric unit having, on the low-pressure axial side, a continuous solid support or body portion and, on the high-pressure axial side, a divergence created by an axially-opening channel extending around the ring and separating radially-inwardly and radially-outwardly facing sealing lips, which project radially beyond the support or body portion. This description refers to the free (pre-installation) condition of the sealing ring. In the-installed condition, the support portion or body need not make contact. Under high-pressure conditions it may sometimes contact the sealed surfaces, but with a lower pressure than the sealing lip and hence without significant sealing function.
The axially-open channel between the sealing lips (or behind the sealing lip, if there is only one) is typically exposed to the fluid pressure on the high-pressure side to assist urging the sealing lip into good sealing engagement.
Another known type of sealing ring has the channel occupied by an insert with very high elasticity which "energises" the sealing lip to some extent, irrespective of the pressure conditions.
Another conventional type of seal is the solid-section or "O-ring" seal, essentially a solid annulus. These seals have the drawback that in some circumstances, the compression required to achieve a desirable degree of sealing results in an undesirably large frictional force.